The goal of the proposed research is (1) the removal of the ionic strength restriction of the various empirical conventions for pH standardization of physiological samples such as plasma, and the justification of the Pitzer ion interaction theory approach to assignment of pH values using the required single ion activity coefficients of the chloride ion in the standard buffers, at an ionic strength I = 0.16 m, similar to that found in serum; (2) adoption of the Pitzer formulation will play an important role for the establishment of a self consistent pH scale; and (3) experimental studies of dissociation equilibria under the "real" conditions at finite ionic strength (as opposed to I = 0.0 m) using electro-chemical cells with and without liquid junction for electromotive-force measurements. The long-term goal is to greatly improve the state of pH measurements for primary reference standards with uncertainties less than or equal too .002. Utilizing isotonic saline as a simple matrix, eight new biological systems are chosen for study in the initial stages: (t) MOBS (0.04 m), NaMOBSate (0.04 m); (2) TABS (0.04 m), NaTABSate (0.04 m), (3) HEPBS (0.04 m), NaHEPBSate (0.04 m); and (4) CABS (0.04 m), NaCABSate (0.04 m); and similarly with 0.05 m buffer compositions. It is fundamental to have these data available for wide use in clinical chemistry. The specific aim of the project involves (i) to determine the thermodynamic dissociation constants of MOBS, TABS, HEPBS, and CABS at 5 to 55 degreesC, including 37 degrees C (body temperature), since no data are available in the literature for these important biological buffers; (ii) to calculate pH values for eight useful standard reference solutions (two from each buffer) at ionic strengths similar to those in physiological fluids at temperatures from 5 to 55xC. For example, the solutions have the compositions: (a) 0.04 m MOBS + 0.04 m NaMOBSate + 0.12 m NaCI; and (b) 0.05 m MOBS + 0.05 m NaMOBSate + 0.1t m NaCI; (iii) to minimize the errors from liquid junction potentials by using a highly reproducible flowing junction cell, so that the operational pH values can be ascertained, (iv) to study the quantitative effect of NaCI in saline media on the essential ionic processes which regulate hydrogen ion in body fluids, and (v) to estimate the single ion activity coefficients, based on the Pitzer convention, required for reliable pH values.